Little is known about the precursors and early manifestations of depression. Recent theoretical and empirical work on temperament and mood disorders in adults and children has converged in suggesting that temperamental low positive emotionality (PE) may be a precursor of subsequent depressive disorders. We seek to begin to test this hypothesis by assessing temperament in a large community sample of 3-year old children, examining the relationship between low PE and two better established risk factors for depression, and investigating the stability of PE over a two-year period. Seven hundred and twenty subjects will complete laboratory assessments of temperament, and 396 will be selected for further study, including laboratory assessments of EEG and parent-child interactions;a battery of interview and rating scale measures of temperament and psychopathology in the children and their parents;and a follow-up evaluation atage 5. The project has six specific aims: (1) examine the structure of PE, parse its core components, and distinguish it from the near-neighbor construct of behavioral inhibition (BI);(2) test hypothesized associations between low PE and two other markers of risk for depression: maternal history of mood disorders and asymmetries in EEG activity (decreased left frontal and right parietal activity);(3) investigate the specificity of the low PE-depression relationship by determining whether child low PE is related to non-mood disorders in parents and EEG asymmetries that have been implicated in some forms of anxiety disorders (increased right frontal and right parietal activity) and exploring whether other temperament variables, such as BI, are also associated with a parental history of mood disorders and decreased left frontal and right parietal EEG activity;(4) evaluate the stability of low PE between the ages of 3 and 5, and examine its relationship to BI over time;(5) identify factors that might moderate the developmental trajectory of low PE (and ultimately the development of depression), such as other temperament variables, parental mood disorders, and parenting behavior;and (6) build the foundation for a long-term study that follows the sample into adolescence/young adulthood in order to determine whether low PE at age 3 predicts the subsequent onset of depression.